With this command line you can easily recover your Public IP address.You can then use it in scripts such as to make sure you are using a VPN connection.
A little explanation is needed: The wget command is a free download manager. it is from the GNU project, it allows downloading files on advanced networks and the Internet. For example, it can create mirror sites, or perform recursive downloads. Its name comes from World Wide Web and GET is the command name used in the HTTP protocol to retrieve a file. It is able to communicate with the HTTP and FTP. (Source Wikipedia)